This invention relates to a process for manufacturing, as end product, a heat-hardenable meltable mixture capable of forming thermosetting resins; in a further aspect the invention relates to a plant for carrying out the aforesaid novel process, and in a third aspect such plant comprises a novel feeding chamber for introducing a pre-mixture of certain components of the above-mentioned mixture into an extruder being part of the plant.
Preferably, the process according to the invention serves for the manufacture of hot melt mixtures solid at room temperature (20.degree. C.), which are hardenable to form thermosetting resins, and in particular for the manufacture of so-called reactive hot melt adhesives.
Meltable mixtures which also comprise sealing and compression-molded material were hitherto manufactured by firstly preparing, for instance in a melt-flow process, a preliminary mixture or pre-mix of finest-ground solid resin, adding thereto optionally liquid resin filler, colorants, lubricating and separating agents which pre-mix was then discontinuously or continuously processed in a roller assembly or an extruder (see "Ullmanns Encyklopadie der technischen Chemie", 4.sup.th edition, vol. 19, page 414).
In known processes of manufacture, the components are also melted down in heated agitator vessels and subsequently processed in tabletting or granulating apparatus to obtain packageable end products. Such processing requires working the viscous melt in kneader-type masticators or extruders with, when the viscosity of the melt is high, correspondingly high power input (Ullmann, ibid, vol. 14, page 237).
Industrial practice demands that there are added to the system constituted by resin and hardening agent various additive components which, depending on specifications demanded by a customer, impart to the heat-hardenable, meltable mixture a number of required properties. Such additive compounds can be hardening catalysts, adhesion-adjusting agents, plasticizers, thixotropy-controlling agents, agents imparting electrical conductivity and fillers.
In the German Offenlegungsschrift 2,533,195 there is described an extruder for continuously extruding heat-hardenable resins which avoids the preparation of pre-mixtures. To this end, heat-hardenable resins are fed together with inert additives such as fillers or plasticizers directly into the extruder.
In the German Offenlegungsschrift 1,954,214 there is disclosed a process for the manufacture of masses in which each of the components is dosed individually, and the work-up of all components takes place in a single extruder. The different components are individually successively introduced into the extruder along the processing pass through the latter.
In the above-named publications there is neither any mention of a combination of heat-hardenable resins with hardening agents, nor a discussion of problems arising from such combination.
In the German Offenlegungsschrift 2,404,658 there is described a process for the continuous compression molding of heat-hardenable resins, in which a heat-hardenable mass is passed through an extruder, and the extruded resin mixture is hardened in a hardening mold under certain conditions. Combinations of resins and hardening agent are prepared in this known process and fed into the extruder. There is no suggestion of a separate introduction of a resin component into the extruder and a subsequent feeding into the latter of a pulverulent hardening agent.
In the heat-hardenable meltable resin-and-hardening agent mixtures according to the invention there is used as a hardening agent a heat-activatable hardener which is inactive at room temperature (about 20.degree. C.).
When preparing the necessary preliminary mixtures or "pre-mixtures" according to a process used by us, it was found to be difficult to obtain the necessary fluidity of all components so that, in practice, planet stirrers, mills, in particular impact disc mills, sieves, drum mixers, three-roller mills and kneading apparatus, and in certain cases granulators had to be installed ahead of the preferably used extruder.
Moreover, the melting of a pre-mixture in which a heat-activatable hardener is present, is only possible if all solid components present therein have melting points below the hardening temperature.